This application makes reference to, claims all rights of priority accruing under 35 U.S.C. xc2xa7119, and incorporates the same herein, from my patent application entitled Cooling Apparatus Used In Fabrication Of Optical Fiber Preform earlier filed in the Korean Industrial Property Office on Sep. 13, 1996, and there duly assigned Serial No. 39868/1996 by that Office.
1. Field of the Invention
The present invention concerns an apparatus and a process for fabricating an optical fiber preform by modified chemical vapor deposition (MCVD), and more particularly an apparatus and a process for uniformly cooling a quartz tube used in fabrication of an optical fiber used generally or as a light amplifier to directly amplify an optical signal.
2. Description of the Related Art
Since the intensity of an optical signal is usually reduced when transmitted through a long distance or divided into several branches, it is required to amplify the optical signal by using a semiconductor or light amplifier. The light amplifier is widely and essentially used in an ultra high speed communication network, generally employing erbium (Er) added optical fiber as a medium for internally amplifying the optical signal. The erbium added optical fiber is fabricated by using modified chemical vapor deposition (MCVD).
Contemporary practice in the art typically relies upon the flow of a raw gas through a quartz tube while the quartz tube is rotated and heated. The raw gas experiences a chemical reaction and deposits particles on the inside of the quartz tube. The burner is moved in the direction of gas flow in order to precipitate the deposition of the particles along the inside the quartz tube. Meanwhile, the deposited particles are sintered by the heat of the moving burner to form a glass phase.
In order to obtain an optical fiber preform for a light amplifier a process such as liquid penetration, gaseous state addition or sol-gel is used with a liquid penetration process forming a porous layer over the core layer. A cooling apparatus is used behind the burner to form the porous layer after formation of the clad layer.
In glass tubing fabrication, efforts such as P. J. H. Prohaskzka, et al., U.S. Pat. No. 3,260,586 teach water cooling via streams applied at acute angles opposite to and against the direction of travel of hot glass tubing. I believe that this is not suitable for optical fiber fabrication however. U.S. Pat. No. 4,576,622 to Lothar Jung for the Manufacture OfPreforms for energy Transmitting Fibers, for example, a travelling cooling apparatus is used to provide downstream cooling during the modified chemical vapor deposition process while in the Method And Apparatus For Fabricating An Oval Cross-Sectional Optical Waveguide, of Dieter Weber, U.S. Pat. No. 5,366,530 for example, nozzles direct cooling gases from two diametrically opposite sides of the tube. Generally, I have found that contemporary cooling processes cause non-uniform cooling of the inside of the quartz tube because of the coolant is ejected in a single direction towards the quartz tube, so that the finally obtained optical fiber has a distribution of non-uniform refractive index, increasing the reflective loss of the optical fiber.
Other contemporary cooling techniques sometimes used to manufacture a porous layer use an annular tube for supplying coolant through a plurality of nozzles radially mounted along the inner perimeter of the annular tube to eject the coolant towards the quartz tube. These contemporary fabrication designs such as the gas curtain devices used in the Method And Apparatus For Drawing Optical Fiber of K. Imoto, et al, U.S. Pat. No. 4,101,300; the Apparatus For Producing Optical Fiber of K. Imoto et al., U.S. Pat. No. 4,123,242, and the plenum for the Method And Apparatus For Making, Coating and Cooling Lightguide Fiber of Un-chul Paek, U.S. Pat. No. 4,594,088, as well as the later efforts shown in the Method And Apparatus For Producing Optical Fiber of H. Takimoto and K. Sakamoto, U.S. Pat. No. 4,894,078 using a continuous helical spiral to provide cooling, seem to be particularly cumbersome due to the difficulty encountered by the need for the cooling stage of the fabrication apparatus to surround a length of the fiber. I have found these designs to be troublesome because it is very difficult to mount the nozzles radially on the inner perimeter of the nozzle support annular tube. Additionally, it is impossible to attach or detach a quartz tube to or from a lathe during processing because the nozzle support annular tube is made of a single continuous ring.
It is an object of the present invention to provide an improved optical fiber, process and apparatus for manufacturing optical fiber.
It is another object to provide a cooling apparatus for uniformly ejecting a coolant towards the outside of a quartz tube so as to form a uniform porous layer in the quartz tube.
It is still another object to provide a process and apparatus for manufacturing optical fiber for a light amplifier having an uniform refractive index.
It is yet another object to provide a cooling apparatus having a simple structure that enhances productivity.
It is still yet another object to provide a cooling apparatus for allowing for quick and easy attachment and detachment of a quartz tube during processing.
It is a further object of the present invention to provide a cooling apparatus uniformity ejecting a coolant towards a part of a quartz tube.
It is a still further object to provide a cooling apparatus for improving the deposition efficiency of the porous layer when fabricating a optical fiber preform by using modified chemical vapor deposition.
According to one aspect of the present invention, an apparatus for cooling a quartz tube used in fabrication of an optical fiber preform by modified chemical vapor deposition may be constructed with a circular plenum supplied with a coolant, and constructed with at least two pivotably separatable, semicircular vent sections readily accommodating detachment and removal of the quartz tube from the chuck of a lathe during processing. The plenum is perforated by a plurality of nozzles formed by orifices arcuately spaced apart along the inside of the vent sections for uniformly ejecting the coolant simultaneously around the entire exterior circumference of the quartz tube passing through the plenum.
According to another aspect of the present invention, an apparatus for cooling a quartz tube used in fabrication of an optical fiber preform by modified chemical vapor deposition may be constructed with a nozzle supplied with a coolant, and constructed with a first and a second vent hollow semicircular sections for accommodating detachment of the quartz tube from the chuck of a lathe. A plurality of vents orifices are formed in arcuate separation along the inside circumferential surface of the semicircular sections for radially ejecting the coolant. A coolant collector receives the coolant ejected out of the vents, while a bracket connected between the nozzle and the coolant collector supports the nozzle. A first connecting arm pivotably connects the first vent section with the bracket, and a second connecting arm pivotably connects the second vent section with the bracket. A coolant supply line supplies the coolant to the nozzle for ejection through the vents. A coolant regulator regulates the coolant supplied to the coolant supply line, and a coolant reservoir stores the coolant flowing out of the coolant collector. The first and second vent sections are pivotally closed together to surround the quartz tube and eject the coolant through the orifices uniformly around the quartz tube mounted on the lathe. The vent sections are hinged and may be readily pivotably opened to enable the quartz tube to be detached from the lathe and removed from the processing line.
The present invention will now be described more specifically with reference to drawings attached only by of example, throughout which same reference numerals are used to represent same functional elements. In addition, detailed descriptions are not made for the conventional parts unnecessary for grasping the inventive concept.